DESCRIPTION: The specific aims of this proposal are to use multidimensional, multinuclear NMR to investigate the structures of telomeric DNA oligonucleotides, including both the simple G-rich telomeres found in diverse species from O. nova to Homo sapiens , as well as the longer and/or irregular repeats found in yeasts, and to study the structure of telomerase RNA and telomerase RNA-DNA duplexes. Three major areas of investigation regarding the structure and formation of telomeres are proposed: (1) Studies of quadruplexes formed by simple telomere repeat oligonucleotides, including the telomere repeats from Oxytricha nova (d(T4G4)), Chlamydomonas (d(T4AG3)), Arabidopsis (d(T3AG3)), Tetrahymena (d(T2G4)), and Homo sapiens (d(T2AG3)) will be continued; (2) The structures formed by oligonucleotides containing single strand telomere repeats from yeasts as well as telomere duplex sequences will be studied; (3) The conformation of sub-domains of the 159 nucleotide Tetrahymena telomerase RNA, specifically (a) helix III, (b) the putative pseudoknot associated with helix III, (c) helix IV, and (d) the RNA template complexed to DNA will be determined. Telomerase is essential for the maintenance of chromosomes ends, which otherwise would shorten with each replication cycle due to the need for an RNA primer on one strand. Currently it is thought that telomerase is inactive in human somatic cells, leading ultimately to chromosome shortening and cell death. On the other hand, telomerase has been found to be active in almost all cancer cells. If this causal relationship between telomerase activity, aging, and cancer hold true, then telomeres and telomerase present important new targets for therapeutic drugs. An understanding of the structure of the nucleic acid components of telomeres and telomerases will be an essential component of such drug design.